Photochemical chlorination of acetonitrile



United States Patent 3,418,228 PHOTOCHEMICAL CHLORINATION 0F ACETONITRILE Philip Lee Bartlett, New Castle County, Del., assignor to E. I. du Pont de Nemours and Company, Wilmington, Del., a corporation of Delaware No Drawing. Filed Jan. 28, 1966, Ser. No. 523,575 7 Claims. (Cl. 204-158) This invention relates to a process for the preparation of trichloroacetonitrile by the photochemical chlorination of acetonitrile, and more particularly to the liquid phase photochemical chlorination of acetonitrile in the presence of a catalyst.

Chlorination of acetonitrile has been investigated in both liquid and vapor phases. Catalytic vapor phase chlorinations are known, utilizing as catalyst a noble metal as described in U.S. Patent No. 2,426,091 or a carbon supported halide of zinc, copper or an alkaline earth metal as described in U.S. Patent No. 2,375,545. However, these vapor phase reactions possess the inherent disadvantage of requiring high temperatures, such as ZOO-400 C., and they also favor the formation of polymers and side products. Vapor phase photochemical chlorination of acetonitrile was reported to be unsuccessful in Bull. Soc. Chem. Belg. 61, 366 (1952).

Liquid phase photochemical chlorination of acetonitrile is described in British Patent 522,835. The main disadvantage of this process is the long induction period. It has been found that no appreciable chlorination occurs in the first 8 hours of exposure to the reaction conditions described.

U.S. Patent No. 2,745,868 describes a liquid phase chlorination without the necessity of using light by reacting chlorine and acetonitrile in the presence of hydrogen chloride. About '25 to 40 hours are necessary for the chlorination and a large amount of hydrogen chloride is required, preferably enough to saturate the acetonitrile. In addition to the unsuitably long reaction time, the large amount of hydrogen chloride required tends to favor the formation of polymers.

It is an object of this invention to provide a liquid phase chlorination which gives good yields of trichloroacetonitrile. Another object is to provide a process for the liquid phase chlorination of acetonitrile which requires only a short reaction time. These and other objects will become apparent from the following description of this invention.

It has now been found that trichloroacetonitrile can be prepared in good yield under mild reaction conditions and short reaction times by reacting acetonitrile and chlorine at 6080 C. in the presence of (l) actinic light, (2) hydrogen chloride and (3) a catalyst selected from the group consisting of mercuric chloride, mercuric acetate, mercuric sulfate, mercuric oxide, aluminum chloride, aluminum fluoride and boron trifluoride etherate and recovering trichloroacetonitrile from the reaction mixture. By the use of the specific catalysts of this invention, satisfactory liquid phase photochemical chlorination can be achieved in a surprisingly short time. In the absence of these catalysts, there is no appreciable chlorination under the same reaction conditions.

The chlorination reaction of this invention follows the equation:

Theoretically about 3 moles of chlorine react with each mole of acetonitrile. It has been found that optimum yields are obtained when the amount of chlorine fed into the system is about 2.5 moles per mole of acetonitrile. As the amount of chlorine is increased to 3 moles, trimerization of the product occurs. When 2.7 moles of chlorine are used, about 5l0% of the product may trimerize. In genice eral, the amount of chlorine should be about 13 moles, and preferably about 2.1-2.5 moles.

The reaction of this invention is carried out in the presence of actinic light. Preferably ultraviolet light is used. A convenient source of ultraviolet light is a mercury vapor lamp.

The chlorination is conducted at about 80 C. Below about 60 C., the reaction is very slow and it is difficult to properly vent the hydrogen chloride formed in the reaction. The accumulation of large excesses of hydrogen chloride tend to favor polymer formation. Temperatures above about 80 C. should be avoided since acetonitrile boils at about 82 C. Preferably temperatures of about 75 C. are employed.

About 15% by weight of hydrogen chloride, based on the acetonitrile, is employed. When less than about 1% of hydrogen chloride is used, some chlorination occurs, but there is a long induction period. More than about 5% is not necessary, since hydrogen chloride is generated during the reaction. Preferably about 1.53% of hydrogen chloride is present.

The catalysts used in accordance with this invention are soluble in acetonitrile and are selected from the group consisting of mercuric chloride, mercuric acetate, mercuric sulfate, mercuric oxide, aluminum chloride, aluminum fluoride and boron trifluoride etherate. Preferably mercuric chloride, mercuric acetate, aluminum chloride or boron trifluoride etherate is employed.

At least about 0.1% by Weight of catalyst, based on the acetonitrile, should be used for satisfactory results. No added benefit is achieved by the use of more than about 10% catalyst, although larger amounts could be used if desired without adversely affecting the reaction. Preferably about 0.255% catalyst is employed.

The process of the invention may be carried out in conventional reaction vessels used for photochemical reactions, for example, a quartz tube. As the source of actinic light, conventional 110 v. low pressure mercury vapor lamps are suitable. Acetonitrile is placed into the quartz tube, a small amount of hydrogen chloride gas and catalyst are introduced and the mixture is heated to 6080 C. Chlorine gas is fed into the system until the desired amount has been added. The resulting reaction mass containing a mixture of trichloroacetonitrile and acetonitrile is then cooled to room temperature. Although the reaction mixture forms an azeotrope upon distillation, acetonitrile can be isolated from the mixture by conventional means known in the art, for example, by distillation with an aliphatic hydrocarbon solvent or by washing the mixture with water.

Conversions, based on the chlorine charged, range from about 2590% depending upon the conditions and catalyst employed. Yields of trichloroacetonitrile of the order of about 6597% are readily achieved in less than about 8 hours. Under the preferred conditions, conversions of about -90%, based on the chlorine charged, and yields of about 97%, based on the conversion, are obtained in about 6 hours or less.

The following examples, illustrating the novel process disclosed herein, are given without any intention that the invention be limited thereto. All parts and percentages are by weight.

EXAMPLES 1-13 General Procedures.Acetonitrile, 70.47 parts, were placed in a quartz tube along with varied amounts of the catalysts disclosed herein. Two parts of anhydrous hydrogen chloride were added. Two -volt low pressure mercury vapor lamps placed two inches from the reactor tube were used as the light source. The mixture was heated to 70i5 C. Chlorine gas was fed into the tube through a sintered blass plate at the rate of 25 parts per hour for six hours, amounting to a total of parts or 1.23 moles of chlorine per mole of acetonitrile. The reactor tube was provided with an outlet for the evolved hydrogen chloride. The outlet gases were fed into Dry Ice/acetone cooled traps to collect any chlorine which failed to react or was quartz tube having only half the volume of the tube used previously. The mole ratio of chlorine to acetonitrile was 2.46: 1. There was essentially no polymeric by-pro-duct formation. The following data were obtained.

swept out of the system by the vented hydrogen chloride. 5

TABLE II CClsCN Catalyst, CClsCN Conversion, percent yield, Example Catalyst percent yield, based 0npercent based on parts based on CHsCN C12 CHaCN CHaCN reacted 14 gcli' 1.5 81.1 84 a9 95 15 HgCh 5.0 86.2 89 73 95 15 Although the invention has been described and exem- The quantity of chlorine consumed was determined by plified by way of specitfic embodiments, it is to be undersubtracting the amount found in the traps from the total stood that it includes all modifications and variations quantity fed into the reactor. The reaction mixture concoming within the scope of the following claims. taining trichloroacetonitrile and acetonitrile was cooled Iclaim: and the trichloroacetonitrile was separated by washing 1. A process for the preparation of trichloroacetonitrile acetonitrile from the mixture with water. Prior to washwhich comprises reacting acetonitrile with chlorine at ing out the unreacted acetonitrile, the mixture was 60-80 C. in the presence of (1) actinic light, (2) hydroanalyzed by vapor phase chromatography to determine gen chloride and (3) a catalyst selected from the group the composition of the reaction mixture. consisting of mercuric chloride, mercuric acetate, mer- For comparison, a Control Run, not within the scope curic sulfate, mercuric ovide, aluminum chloride, alumiof the invention, was carried out following the above num fluoride and boron trifiuoride etherate and recoverprocedure except that no catalyst was added. Hydrogen ing trichloroacetonitrile from the reaction mixture. chloride was added as indicated above. 2. The process of claim 1, in which 1-3 moles of The following table summarizes the results obtained chlorine per mole of acetonitrile, 15% by weight of using the type and amount of catalyst indicated. Assumhydrogen choride, based on acetonitrile, and at least 0.1%

ing 100% chlorine consumption the maximum theoretical conversion of acetonitrile is 41% due to the excess acetonitrile present.

by weight of catalyst, based on acetonitrile, are present. 3. The process of claim 2, in which the temperature is 75 C.

4. The process of claim 3, in which 2.12.5 moles of TABLE I C ClsCN Catalyst, CClsCN Conversion, percent yield, Example Catalyst percent yield, based on percent based on parts based on CHaCN C12 OHsCN CHJCN reacted 0. 25 72. 3 74 30. 7 96 0. 75 76. 5 79 32. 4 95 1. 5 80. 3 83 34. 1 95 5. O 88. 0 91 37. 3 93 0. 75 72. 3 74 30. 7 96 1. 5 79. 1 32. 8 97 5. 0 58. 8 60 24. 6 96 7. 5 78. 7 84 34. 4 92 1. 5 23. 9 35 14. 4 83 5.0 38.1 56 23.0 67 1. 5 29. 8 34 14. 0 86 1. 5 24. 1 32 13.1 74 13 g 1. 5 22. 8 28 11. 5 80 Control None 0 0 0 O 0 A significant amount of diehloroacetonitrile was formed.

From the above table the pronounced catalytic effect of the specified catalysts can be seen. In the Control Run no conversion was obtained. The same result is obtained when both the hydrogen chloride and catalyst are omitted.

EXAMPLES 14-15 The procedure used in Examples 113 was followed except that 35.2 parts of acetonitrile were placed in a References Cited UNITED STATES PATENTS 5/1942 Spence et al. 204-158 XR FOREIGN PATENTS 6/ 1940 Great Britain.

HOWARD S. WILLIAMS, Primary Examiner. 

1. A PROCESS FOR THE PREPARATION OF TRICHLOROACETONITRILE WHICH COMPRISES REACTING ACETONITRILE WITH CHLORINE AT 60-80*C. IN THE PRESENCE OF (1) ACTINIC LIGHT, (2) HYDROGEN CHLORIDE, AND (3) A CATALYST SELECTED FROM THE GROUP CONSISTING OF MERCURIC CHLORIDE, MERCURIC ACETATE, MERCURIC SULFATE, MERCURIC OXIDE, ALUMINUM CHLORIDE, ALUMINUM FLUORIDE AND BORON TRIFLUORIDE ETHERATE AND RECOVERING TRICHLOROACETONILRILE FROM THE REACTION MIXTURE. 